python - 如何从数据库中的树数据结构创建json对象？

Question

我正在使用以下型号的 flask :

class NewsCategory(db.Model):
    __tablename__ = 'news_category'
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(64))
    parent_id = db.Column(db.Integer, db.ForeignKey('news_category.id'))
    children = db.relationship("NewsCategory")

我想从此模型创建一个 json 对象以在导航菜单中使用。

我想递归地解析它并构建一个如下所示的分层 JSON 对象:

tree = [{"title": "Node 1", "id": "1"},
         {"title": "Folder 2", "id": "2", "folder": "true", "children": [
            {"title": "Node 2.1", "id": "3"},
            {"title": "Node 2.2", "id": "4"}
          ]}
        ]

Answer 1

我使用一个名为 Flask-Restless 的库用于查询数据库并返回json。它专为与 SQLAlchemy 一起使用而设计。

如果您不希望与这样的东西集成，您可以对 SQLAlchemy 模型进行子类化，然后在其上运行 to_json() 方法。

类 NewsCategory(db.Model, JsonSerializer)

class JsonSerializer(object):
    """A mixin that can be used to mark a SQLAlchemy model class which
    implements a :func:`to_json` method. The :func:`to_json` method is used
    in conjuction with the custom :class:`JSONEncoder` class. By default this
    mixin will assume all properties of the SQLAlchemy model are to be visible
    in the JSON output. Extend this class to customize which properties are
    public, hidden or modified before being being passed to the JSON serializer.
    """

    __json_public__ = None
    __json_hidden__ = None
    __json_modifiers__ = None

    def get_field_names(self):
        for p in self.__mapper__.iterate_properties:
            yield p.key

    def to_json(self):
        field_names = self.get_field_names()

        public = self.__json_public__ or field_names
        hidden = self.__json_hidden__ or []
        modifiers = self.__json_modifiers__ or dict()

        rv = dict()
        for key in public:
            rv[key] = getattr(self, key)
        for key, modifier in modifiers.items():
            value = getattr(self, key)
            rv[key] = modifier(value, self)
        for key in hidden:
            rv.pop(key, None)
        return rv

信用:Github Overholt project (Flask-Security 的作者)